This application is based on Japanese patent application No. 10-135412 filed on May 18, 1998, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a solid state image pickup device for converting an optical signal into an electrical signal, and more particularly to a solid state image pickup device capable of being used with an image scanner.
b) Description of the Related Art
A line sensor device having a green channel (G-ch) line sensor and a red/blue channel (R/B-ch) line sensor is known, which can pick up color image information as electrical signals. The G-ch line sensor of this line sensor device is used for picking up mainly a luminance signal, whereas the R/B-ch line sensor is used for picking up mainly color signals. Since a resolution of the color signal lower than that of the luminance signal does not pose any serious problem, the numbers of red (R) pixels and blue (B) pixels of the R/G-ch line sensor are each set to have a half of the number of green (G) pixels of the G-channel line sensor. R and B pixels are alternately disposed in line in the R/B-ch line sensor, whereas only G pixels are consecutively disposed in line.
Red and blue color filters are alternately disposed on the pixels (light reception sensors) of the R/G-ch line sensor, whereas green color filters are consecutively disposed on the pixels of the G-ch line sensor. Both the R/B-ch and G-ch line sensors have the same structure excepting color filters.
Since the R/B-ch line sensor generates electric charges of both R and B pixels, it is necessary to set the same charge storage time or integration time to the R and B pixels.
If the color of a subject is deviated to the red side or blue side, this same integration time is not suitable for both the red and blue colors. Therefore, outputs of pixels on one channel (R-ch or B-ch) have always a lower S/N ratio than the other channel.
It is an object of the present invention to provide a solid image pickup device capable of independently controlling an integration time of each of green, red and blue pixels of a color line sensor device having G-ch and R/B-ch line sensors and realizing a high S/N ratio of each color output.
According to one aspect of the present invention, there is provided a solid state image pickup device comprising: a photoelectric conversion element line having a plurality of first and second conversion elements disposed alternately, the first and second photoelectric conversion elements converting light having different colors into electric charges;first transfer means for transferring electric charges generated by the plurality of first photoelectric conversion elements to an external circuit; a first transfer gate for transferring the electric charges generated by the plurality of first photoelectric conversion elements to the first transfer means; a first drain for draining unnecessary electric charges generated by the plurality of first photoelectric conversion elements; a first drain gate for transferring the unnecessary electric charges generated by the plurality of first photoelectric conversion elements to the first drain; second transfer means for transferring electric charges generated by the plurality of second photoelectric conversion elements to an external circuit; a second transfer gate for transferring the electric charges generated by the plurality of second photoelectric conversion elements to the second transfer means; a second drain for draining unnecessary electric charges generated by the plurality of second photoelectric conversion elements; a second drain gate for transferring the unnecessary electric charges generated by the plurality of second photoelectric conversion elements to the second drain; and a controller for independently controlling a charge transfer by the first and second transfer gates or by the first and second drain gates.
According to another aspect of the present invention, there is provided a solid state image pickup device comprising: a photoelectric conversion element line having a plurality of first and second photoelectric conversion elements disposed alternately, the first and second photoelectric conversion elements being sensitive to light of different colors; a line of first charge storage areas disposed adjacent to each of the plurality of first photoelectric conversion elements for storing electric charges photoelectrically converted by the first photoelectric conversion elements; first charge reading means disposed adjacent to the first charge storage area line for reading electric charges stored in the first charge storage area; first transfer means disposed adjacent to the first charge reading means for sequentially transferring the read electric charges to an external circuit; a line of second charge storage areas disposed adjacent to each of the plurality of second photoelectric conversion elements at positions different from the first charge storage area line for storing electric charges photoelectrically converted by the second photoelectric conversion elements; second charge reading means disposed adjacent to the second charge storage area line for reading electric charges stored in the second charge storage area; second transfer means disposed adjacent to the second charge reading means for sequentially transferring the read electric charges to an external circuit; first charge draining means disposed adjacent to each charge storage area of the first charge storage area line for draining electric charges in the first charge storage area; and second charge draining means disposed adjacent to each charge storage area of the second charge storage area line for draining electric charges in the second charge storage area.
The photoelectric conversion element line with first and second photoelectric conversion elements for generating color signals is provided with the first and second charge draining means for draining electric charges stored in the photoelectric conversion elements, independently for the first and second photoelectric conversion elements. Accordingly, the charge storage time or integration time can be controlled independently for the first and second photoelectric conversion elements.
It is possible to independently set an optimum integration time of each color and generate a color signal with an improved S/N ratio.